(1) Field of the Invention
The present invention relates to a method and a device for simulating a failure on an aircraft. The method of the invention is intended more particularly to simulate a turbine engine failure on a rotary wing aircraft having at least two engines.
(2) Description of Related Art
During this type of failure, the aircraft has only one engine left delivering power. However with only one engine it is clearly not possible to reach a power level that corresponds to the maximum power level from two engines.
The aircraft is thus in a degraded mode of operation in which the total power available is less than the power delivered by both engines. Nevertheless, in particular stages of flight, such as when hovering or landing, a rotary wing aircraft requires a large amount of power.
For this purpose, the degraded mode of operation includes several supercontingency power ratings:
a first contingency rating associates a supercontingency power referred to as 30-sec OEI (one engine inoperative) that is usable for a duration of the order of thirty consecutive seconds, this first contingency rating being usable for about three times during a flight;
a second contingency rating associates a maximum contingency power referred to as 2-min OEI and is usable for a duration of about two minutes; and
a third contingency rating associating an intermediate contingency power referred to as OEIcontinuous, which power is usable for a duration extending to the end of the flight, for example.
The 30-sec OEI first contingency rating and the 2-min OEI second contingency rating can be used for limited lengths of time only. The powers of these ratings are well above the power delivered by an engine in normal operation and using either of these two ratings requires the aircraft to be overhauled as a consequence. However, exceeding those recommended utilization times can lead to even greater and possibly immediate degradation of the engine or of the power transmission means, e.g. the rotors providing lift and also propulsion.
The 30-sec OEI, 2-min OEI, and OEIcontinuous contingency ratings are controlled by an electronics control unit of the engine. Each engine is connected to such a control unit, which is commonly referred to as an electronic engine control unit (EECU). EECUs also possess connections with each other enabling them to exchange information about the operation of the engines.
The powers associated with each contingency rating are determined as a function of flight conditions, i.e. the pressure and the temperature outside the aircraft, corresponding to the pressure and the temperature of the air being fed to the engines, and also the speed and the altitude of the aircraft.
In order to train aircraft pilots in this type of failure and in the associated degraded mode of operation, rotary wing aircraft generally have a “training” mode available. This training mode makes it possible to simulate the total failure of one engine.
When training mode is activated, conventionally by means of a switch on the instrument panel of the aircraft, the control unit of each engine reduces the power from the two engines so that the overall power from both engines corresponds to the 30-sec OEI supercontingency power of the first contingency rating. The term “low overall power” is used below to designate this combined power from both engines in training mode.
In training mode, two configurations are possible for obtaining this low overall power. Firstly, the power may be shared uniformly between both engines.
The training mode may also simulate a total failure of one engine more closely, in particular by running a first engine at an idling speed in which it nevertheless delivers some minimum power level. Under such circumstances, the switch on the control panel has two positions, corresponding to simulating failure on each of the engines. The power delivered by the second engine is then raised to a value close to the intermediate contingency power OEIcontinuous of the third contingency rating, in general up to 5% below that power. This 5% margin serves to avoid degrading the engine and the associated transmission means. The remaining 5% of the power needed to reach the low overall power for the aircraft is delivered by the first engine at its idling speed.
Once training mode has been activated, the power of the aircraft is limited to this low overall power so that the pilot is trained in this degraded mode of operation. The contingency ratings 30-sec OEI, 2-min OEI, and OEIcontinuous are then simulated in this degraded mode of operation.
Nevertheless, the training mode has several drawbacks.
Firstly, the weight of the aircraft is not variable, with tables defining flight envelopes that are authorized during such training as a function of the weight. The weight of the aircraft is taken into account by the control unit in order to determine the low overall power level.
Also, training mode simulates only the total failure of one engine. It is not possible, for example, to simulate a partial loss of power from one engine or an accidental flameout of an engine.
Furthermore, since training mode simulates only and precisely the total failure of one engine, the training cannot be carried out progressively, e.g. to accommodate a trainee's level of competence and progress.
Finally, the power developed by an engine tends to decrease over time. The power developed by a new turbine engine is greater than the power developed by an older engine. As a result, the contingency powers available in a degraded mode of operation are different depending on whether the engine is new or old.
Only one configuration can be used in the training mode of an aircraft, corresponding to an aircraft weight and to contingency rating powers that are imposed by flight conditions and by the aging state of the engine.
Also known is document US 2009/0186320, which describes a system enabling a total failure of one engine to be simulated for different configurations. Those configurations are predefined as a function of flight conditions, such as the outside temperature and pressure or the altitude of the aircraft. That system also serves to adapt the power available for training as a function of the total weight of the aircraft but only for two types of loading. That system thus enables several different types of training to be simulated, but the power made available is calculated from predetermined criteria and therefore cannot be adapted, in particular to the competence of the trainee.
Furthermore, document US 2002/133322 describes a method of simulating the failure of one engine in which the power available for simulation is obtained by reducing the power of a first engine for which the failure is being simulated. The power from the second engine is then increased in order to reach the required power level. The distribution of power is thus not uniform between the two engines. In the event of a real failure of the second engine, the reaction time of the first engine, which is idling, can leave the aircraft in a dangerous situation.
Document US 2005/234689 describes a method of simulating the failure of one engine by using different acceleration relationships for the two engines of the aircraft. The combination of those accelerations corresponds to the accelerations that would be provided by a single engine in the event of the failure of the other engine. Furthermore, the power from each engine is reduced so as to have a power margin available in the event of a real failure of one engine.
Document U.S. Pat. No. 5,873,546 describes a method and a system for simulating a failure of one engine for various different configurations. A switch serves in particular to select the failure mode that is to be simulated, from among the three ratings: 30-sec OEI; 2-min OEI; and OEIcontinuous. That method also makes it possible to select the total loaded weight of the aircraft that it is desired to simulate.
Finally, document U.S. Pat. No. 4,831,567 describes a method of simulating the failure of one engine in which the total power available for simulation can be obtained by reducing either the power from a single engine on which the failure is being simulated, or the power from both engines in an equivalent manner. Power distribution is thus not necessarily uniform between the two engines, in particular concerning the power delivered by a first engine on which the failure is being simulated, with that power being reduced while the power from the other engine is increased in order to reach the total power level required for the simulation.